The broad objective of my research has been to elucidate the neural and hormonal factors involved in the normal contractile and secretory functions of the lactating mammary gland. My efforts over the next several years will be: 1. To analyze the relative roles of the mammary gland, kidney, and liver in the metabolic clearance of immunoreactive prolactin from the plasma of rats during late pregnancy and during lactation. Metabolic clearance rate will be assessed by the constant infusion to steady-state method. 2. To determine the rate and extent of transfer of immunoreactive prolactin (through the milk) from mother to offspring throughout lactation. 3. To determine the factors involved in the development and maintenance of the multiphase pattern of prolactin secretion. 4. To analyze the role of exteroceptive mechanisms in the regulation of prolactin secretion. 5. To analyze the role of peripheral mechanisms in inhibiting the milk stimulatory effects of prolactin and to determine to what extent they contribute to decline of mammary secretion. 6. To investigate with sensitivity intramammary pressure techniques whether estrogen and progesterone exert either facilitatory and/or inhibitory influences at the mammary gland level upon the contractile response of the mammary gland myoepithelium. 7. To analyze the role of the cerebral cortex and the sympathetic nervous system in the regulation of mammary contraction.